SW-846 Update V 3572 - 1 Revision 1 

July 2014 

 METHOD 3572 

EXTRACTION OF CHEMICAL AGENTS FROM WIPE SAMPLES USING 

MICROEXTRACTION

 SW-846 is not intended to be an analytical training manual. Therefore, method 

procedures are written based on the assumption that they will be performed by analysts who are 

formally trained in at least the basic principles of chemical analysis and in the use of the subject 

technology. 

 In addition, SW-846 methods, with the exception of required method use for the analysis 

of method-defined parameters, are intended to be guidance methods which contain general 

information on how to perform an analytical procedure or technique which a laboratory can use 

as a basic starting point for generating its own detailed standard operating procedure (SOP), 

either for its own general use or for a specific project application. The performance data 

included in this method are for guidance purposes only, and are not intended to be and must not 

be used as absolute QC acceptance criteria for the purposes of laboratory accreditation. 

1.0 SCOPE AND APPLICATION 

 1.1 This method describes the extraction of chemical agents from wipe samples using 

a microextraction technique. The following compounds have been determined by this method: 

Compound Name CAS No.a

GB (o-Isopropyl methylphosphonofluoridate) 107-44-8 

VX (O-Ethyl S-2-diisopropylaminoethyl methyl phosphonothiolate) 50782-69-9 

HD [Bis(2-chloroethyl)sulfide] 505-60-2 

aChemical Abstracts Service Registry Number 

Additionally, this method may be applicable to other chemically similar compounds and 

chemical agent degradation products. For a summary of changes in this version, please see 

Appendix A at the end of this document. 

 1.2 Other solvent systems may be employed in place of those described here. For any 

solvent system used, including those mentioned in the method, one needs to demonstrate 

adequate performance for the analytes of interest. 

 1.3 There is a risk to the analyst of exposure to chemical agents. The analyst should 

pay special attention to the safety information in Sec. 5.0. 
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 1.4 Prior to employing this method, analysts are advised to consult the base method 

for each type of procedure that may be employed in the overall analysis (e.g., Methods 3500, 

3600, 5000, and 8000) for additional information on quality control procedures, development of 

QC acceptance criteria, calculations, and general guidance. Analysts also should consult the 

disclaimer statement at the front of the manual and the information in Chapter Two for guidance 

on the intended flexibility in the choice of methods, apparatus, materials, reagents, and 

supplies, and on the responsibilities of the analyst for demonstrating that the techniques 

employed are appropriate for the analytes of interest, in the matrix of interest, and at the levels 

of concern. 

 In addition, analysts and data users are advised that, except where explicitly specified in a 

regulation, the use of SW-846 methods is not mandatory in response to Federal testing 

requirements. The information contained in this method is provided by EPA as guidance to be 

used by the analyst and the regulated community in making judgments necessary to generate 

results that meet the data quality objectives for the intended application. 

 1.5 This method is restricted to use by, or under supervision of, appropriately 

experienced and trained personnel. Each analyst must demonstrate the ability to generate 

acceptable results with this method. 

 1.6 WARNING: The toxicity of these chemical warfare agents presents the worker with 

hazards unfamiliar to most experienced laboratory personnel. Special techniques and 

precautions must be used even for the simplest procedures involving these agents (see Ref. 1 

for additional guidance). 

2.0 SUMMARY OF METHOD 

 2.1 This method provides the procedures for sample collection and extraction of the 

referenced compounds from wipe samples. A separate extract will be required for each agent 

to be analyzed. 

 2.2 Materials are surface wiped using a gauze pad (2” x 2” pad). After wiping a 

surface area, usually 10 cm x 10 cm, the pad is placed into a labeled vial. 

 2.3 Samples are extracted with 4 mL of 10% 2-propanol (IPA) in dichloromethane by 

vortex mixing and filtered, if necessary. 

 2.4 An optional water wash is included for VX that back-extracts the compound from 

heavy organics that would interfere with the assay. An optional column cleanup procedure 

utilizes a Carboprep90 column and a silica column to separate GB from heavy organics, if 

needed. Suitable solvents are used to elute the extract first through the Carboprep90 column, 

then the silica column. 

3.0 DEFINITIONS 

 Refer to Chapter One and the manufacturer's instructions for definitions that may be 

relevant to this procedure. 
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4.0 INTERFERENCES 

 4.1 Solvents, reagents, glassware, and other sample processing hardware may yield 

artifacts and/or interferences to sample analysis. All of these materials must be demonstrated 

to be free from interferences under the conditions of the analysis by analyzing method blanks. 

Specific selection of reagents and purification of solvents by distillation in all-glass systems may 

be necessary. Refer to each method to be used for specific guidance on quality control 

procedures and to Chapter Four for general guidance on the cleaning of glassware. Also refer 

to the determinative methods to be used for information regarding potential interferences. 

 4.2 Other phosphorous- and sulfur-containing compounds can interfere with the 

method performance and affect the result. 

 4.3 Interferences that can cause the chemical agents to decompose include moisture, 

light, elevated temperatures, and an improper extraction solvent pH range. The stability of the 

chemical agents noted in this method is contingent on maintaining the pH ranges as indicated in 

Sec. 8.2. 

 4.4 Samples with high organic loading can mask or elute with the agent analyte. 

5.0 SAFETY 

WARNING: The toxicity of these chemical warfare agents presents the worker with hazards 

unfamiliar to most experienced laboratory personnel. Special techniques and precautions must 

be used even for the simplest procedures involving these agents. 

 5.1 This method does not address all safety issues associated with its use. The 

laboratory is responsible for maintaining a safe work environment and a current awareness file 

of OSHA regulations regarding the safe handling of the chemicals listed in this method. A 

reference file of material safety data sheets (MSDSs) should be available to all personnel 

involved in these analyses. 

 5.2 Personal protective equipment (PPE) requirements include safety glasses, lab 

coat, and protective gloves. The availability of emergency response equipment and support 

personnel should be as indicated in a laboratory chemical hygiene plan. 

 5.3 Exposure to chemical agent material is possible from contact. Respiratory 

exposure can result from spills or improper use of ventilation control. 

 5.4 Risk is primarily associated with compromise of protective gloves. Compromise is 

most likely to occur as agent vials are opened. 

6.0 EQUIPMENT AND SUPPLIES 

 6.1 The mention of trade names or commercial products in this manual is for illustrative 

purposes only, and does not constitute an EPA endorsement or exclusive recommendation for 
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use. The products and instrument settings cited in SW-846 methods represent those products 

and settings used during method development or subsequently evaluated by the Agency. 

Glassware, reagents, supplies, equipment, and settings other than those listed in this manual 

may be employed provided that method performance appropriate for the intended application 

has been demonstrated and documented. 

 This section does not list all of the common laboratory glassware (e.g., beakers and 

flasks) that might be used. 

 6.2 Personal protective equipment 

 6.3 Vials, 1-, 3-, and 6-dram for sample collection 

 6.4 Vials, 1-dram for extracts 

 6.5 Gauze pads, non sterile, 100% cotton, approximately 2” x 2” or 4” x 4” squares 

available Edwards Medical Supply, or a suitable equivalent. For each sampling event or a 

specific project application gauze pads from the same manufacturing lot should be used. 

 6.6 Analytical balance, capable of measuring to the nearest mg 

 6.7 Pasteur pipettes, 5 3⁄4,” Fisherbrand, or equivalent 

 6.8 Syringes, 10-μl and 50-μl used for preparing spikes and surrogates 

 6.9 Volumetric glassware, 2-, 5-, and 10-mL used for preparing spikes and surrogates 

 6.10 BD syringe filter (10-mL Luer-Lok) 

 6.11 Whatman nylon syringe filter, 0.45-μm pore size, or equivalent 

 6.12 Vortex mixer, benchtop, or as noted in Sec. 6.13 

 6.13 Centrifuge, benchtop 

 6.14 pH test strips 

7.0 REAGENTS AND STANDARDS 

 7.1 Reagent-grade chemicals must be used in all tests. Unless otherwise indicated, it 

is intended that all reagents conform to the specifications of the committee on Analytical 

Reagents of the American Chemical Society, where such specifications are available. Other 

grades may be used, provided it is first ascertained that the reagent is of sufficiently high purity 

to permit its use without lessening the accuracy of the determination. 

 7.2 Dichloromethane (DCM), CH2Cl2, optima grade or equivalent 

 7.3 2-Propanol (IPA), (CH3)2CHOH, optima grade or equivalent 

 7.4 1 N Sodium hydroxide, NaOH 
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 7.5 Sodium chloride, NaCl 

 7.6 Saturated Glacial Acetic Acid/NaCl solution. Dissolve 7 g of NaCl in 35 mL of glacial 

acetic acid in a 40-mL vial 

 7.7 Isopropyl methylphosphonofluoridate; Sarin (GB) 

 7.8 O-ethyl S-(2-diisopropylaminoethyl)methylphosphonothioate (VX) 

 7.9 Bis(2-chloroethyl)sulfide (HD) 

 7.10 Diisopropyl fluorophosphonate (DFP), C6-H14-F-O3-P 

 7.11 2-Chloroethyl ethyl sulfide (CEES), C4-H9-Cl-S 

 7.12 Diethyl ethylthiophosphonate (DEETP) 

8.0 SAMPLE COLLECTION, PRESERVATION AND STORAGE 

Sample collection, preservation and storage requirements may vary by EPA program and 

may be specified in a regulation or project planning document that requires compliance 

monitoring for a given contaminant. Where such requirements are specified in the regulation, 

follow those requirements. In the absence of specific regulatory requirements, use the following 

information as guidance in determining the sample collection, preservation and storage 

requirements. 

 8.1 This method is a microextraction technique in which a particular surface area is 

wiped with either a 2” x 2” or 4” x 4” gauze pad and extracted with 4.0 mL of 10% IPA in DCM. 

Because of this, sample collection plans should consider sufficient replicates. 

 8.2 Holding times 

 8.2.1 Samples for GB, HD and VX assay must be extracted within 7 days 

 of collection. Extraction times of less than 3 days are preferred. Extracts must be 

 analyzed within 14 days of extraction. 

 8.2.2 GB undergoes rapid hydrolysis to form hydrogen fluoride, isopropyl 

 methyl phosphonic acid and other compounds. Conditions of pH within a range of 3.5 to 

 5 will slow this decomposition rate. Stability in organic extracts exceeds 28 days. 

 8.2.3 HD undergoes hydrolysis to form thiodiglycol and other compounds. 

 Conditions of pH within a range of 3.5 to 5 will slow decomposition rate. Chloride ion 

 can be added to reduce the effects of metal cations. Stability in organic extracts 

 exceeds 28 days. 

 8.2.4 VX undergoes very rapid hydrolysis under extremely basic conditions, 

with a half-life of 16 minutes at pH 13 and 1.3 minutes at pH 14. Optimal pH for VX 

stability (for a half-life of approximately 350 days) was determined to be within a range of 8 

to 9. Stability in organic extracts exceeds 28 days. Partitioning is present with non-polar 
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solvents (hexane). 

 8.3 Sample collection 

 The exact number of samples that may be necessary for a particular sampling event, such 

as possibly collecting samples in duplicate, should be documented in the appropriate project 

planning documents. It is also important to understand that duplicate wipe samples may not 

always yield consistent results for precision purposes. 

 8.3.1 Place 1 mL of IPA onto gauze pad. 

 8.3.2 Wipe a surface area of 10 cm x 10 cm. 

 8.3.3 Place the gauze pad into a labeled vial. 

 8.3.4 Record the vial identification number on the chain of custody and the 

sample label. 

 8.3.5 One additional sample from the same general location should be 

designated as a duplicate for each group of twenty or fewer samples. Two empty 

vials designated as a blank and LCS, both containing a clean IPA-soaked gauze 

pad added at the time of sample collection, should be returned with each group of 

twenty or fewer samples. 

9.0 QUALITY CONTROL 

 9.1 Refer to Chapter One for guidance on quality assurance (QA) and quality control 

(QC) protocols. When inconsistencies exist between QC guidelines, method-specific QC 

criteria take precedence over both technique-specific criteria and those criteria given in Chapter 

One and technique-specific QC criteria take precedence over the criteria in Chapter One. Any 

effort involving the collection of analytical data should include development of a structured and 

systematic planning document, such as a Laboratory/Monitoring Quality Assurance Plan 

(LMQAP) or a Sampling and Analysis Plan (SAP), which translates project objectives and 

specifications into directions for those that will implement the project and assess the results. 

Each laboratory should maintain a formal quality assurance program. The laboratory should 

also maintain records to document the quality of the data generated. All data sheets and quality 

control data should be maintained for reference or inspection. 

 9.2 Initial demonstration of proficiency and lower limit of quantitation (LLOQ) 

Each laboratory must demonstrate initial proficiency with each sample preparation and 

determinative method combination it utilizes by generating data of acceptable accuracy and 

precision for target analytes in a clean matrix. The laboratory must also repeat the 

demonstration of proficiency whenever new staff members are trained or significant changes in 

instrumentation are made. See Method 8000D, Sec. 9.3 for information on how to accomplish a 

demonstration of proficiency. 
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The laboratory shall establish the LLOQ as the lowest point of quantitation, which in most 

cases, is the lowest concentration in the calibration curve. LLOQ verification is recommended 

for each project application to validate quantitation capability at low analyte concentration levels. 

An LLOQ check standard (not part of an initial calibration) is prepared by spiking a clean control 

material with the analyte(s) of interest at the predicted LLOQ concentration level(s). The LLOQ 

check is carried through the same preparation procedures as environmental samples and other 

QC samples. Recovery of target analytes in the LLOQ check standard should be within 

established in-house limits, or other such project-specific acceptance limits, to demonstrate 

acceptable method performance at the LLOQ. Until the laboratory has sufficient data to 

determine acceptance limits, the LCS criteria ± 20% may be used for the LLOQ acceptance 

criteria. Additional information on LLOQ can be found in 8000D, Section 9.7. 

 9.3 Initially, before processing any samples, the analyst should demonstrate that all 

parts of the equipment in contact with the sample and reagents are interference-free. This is 

accomplished through the analysis of a method blank. As a continuing check, each time 

samples are extracted, cleaned up, and analyzed, and when there is a change in reagents, a 

method blank should be prepared and analyzed for the compounds of interest as a safeguard 

against chronic laboratory contamination. 

 9.4 Any method blanks, matrix spike samples, or replicate samples should be 

subjected to the same analytical procedures (Sec. 11.0) as those used on actual samples. 

 9.5 Standard quality assurance practices should be used with this method as included 

in appropriate systematic planning documents and laboratory SOPs. All instrument operating 

conditions should be recorded. 

 9.6 Also see Method 3500 for QC procedures related to extraction and sample 

preparation procedures and refer to the determinative methods to be used for determinative QC 

procedures. 

 9.7 As noted earlier, use of any extraction technique, including solvent extraction, 

should be supported by data that demonstrate the performance of the specific solvent system 

and operating conditions for the analytes of interest, at the levels of interest, in the sample 

matrix. 

 9.8 All field and QC samples should be spiked with an appropriate mix of surrogate 

compounds, if available, in order to track extraction efficiency. 

 9.9 Any reagent blanks, matrix spike, and replicate samples should be subjected to 

exactly the same analytical procedures as those used on field samples. 

10.0 CALIBRATION AND STANDARDIZATION 

 Calibration is not required for this method. 

11.0 PROCEDURE 

 11.1 Spike the matrix spike, matrix spike duplicate or laboratory control spike (LCS) 
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with agent. Record spike amounts into controlled notebook. 

 11.1.1 Suggested GB spike is 40 ng. 

 11.1.2 Suggested VX spike is 40 ng. 

 11.1.3 Suggested HD spike for FPD is 120 ng and for GC/MS is 40 ng. 

 11.2 Spike all samples with appropriate surrogates. 

 11.2.1 Suggested 40 ng of DFP for GB samples. 

 11.2.2 Suggested 40 ng of DEETP for VX samples. 

 11.2.3 Suggested 120 ng of CEES for HD FPD and 40 ng for GC/MS. 

 11.3 Add 4.0 mL of 10% IPA in dichloromethane to all samples. For VX samples, add 

200 μL of 1N sodium hydroxide solution to ensure that the extract is basic, taking care not to 

overshoot desired pH. More sodium hydroxide may be used if needed. The pH range for VX 

should be between 8-10. 

 11.3.1 Check pH with pH paper. 

 11.3.2 Mix on a vortex mixer for 30 seconds. 

 11.3.3 Centrifuge the sample for 1 minute at 2000 rpm, if necessary. 

 11.3.4 If filtration is necessary, filter the solvent extract into another vial. 

 11.3.5 Store the extract in a refrigerator at <6 °C until analysis. 

12.0 DATA ANALYSIS AND CALCULATIONS 

 There are no determinative data analysis and calculation steps directly associated with 

this procedure. Follow the directions in the determinative method. 

13.0 METHOD PERFORMANCE 

 13.1 Performance data and related information are provided in SW-846 methods only as 

examples and guidance. The data do not represent required performance criteria for users of 

the methods. Instead, performance criteria should be developed on a project-specific basis, 

and the laboratory should establish in-house QC performance criteria for the application of this 

method. These performance data are not intended to be and must not be used as absolute QC 

acceptance criteria for the purposes of laboratory accreditation.

 13.2 Refer to the appropriate determinative method for performance data examples and 

guidance. 
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14.0 POLLUTION PREVENTION 

 14.1 Pollution prevention encompasses any technique that reduces or eliminates the 

quantity and/or toxicity of waste at the point of generation. Numerous opportunities for pollution 

prevention exist in laboratory operations. The EPA has established a preferred hierarchy of 

environmental management techniques that places pollution prevention as the management 

option of first choice. Whenever feasible, laboratory personnel should use pollution prevention 

techniques to address their waste generation. When wastes cannot be feasibly reduced at the 

source, the Agency recommends recycling as the next best option. 

 14.2 For information about pollution prevention that may be applicable to laboratories 

and research institutions consult Less is Better: Laboratory Chemical Management for Waste 

Reduction, a free publication available from the American Chemical Society (ACS), Committee 

on Chemical Safety. 

http://portal.acs.org/portal/fileFetch/C/WPCP_012290/pdf/WPCP_012290.pdf. 

 15.0 WASTE MANAGEMENT 

 The Environmental Protection Agency requires that laboratory waste management 

practices be conducted consistent with all applicable rules and regulations. The Agency urges 

laboratories to protect the air, water, and land by minimizing and controlling all releases from 

hoods and bench operations, complying with the letter and spirit of any sewer discharge permits 

and regulations, and by complying with all solid and hazardous waste regulations, particularly 

the hazardous waste identification rules and land disposal restrictions. For further information 

on waste management, consult the ACS publication listed in Sec. 14.2. 

16.0 REFERENCES 

1. Applicable documents to support the occupational health program when dealing with 

 chemical agents include AR11-34 (The Army Respiratory Protection Program; AR 40-5 

 (Preventive Medicine); DA Pam 40-8 (Occupational Health guidelines for the evaluation 

 and Control of Occupational Exposure to Nerve Agents GA, GB, GC, and VX.) and DA 

 Pam 40-173 (Occupational Health Guidelines for the Evaluation and Control of 

 Occupational Exposure to Mustard Agents H, HD, and HT). 

2. Development and Evaluation of an Analytical Method for Determination of GB, VX, and 

 HD in Concrete, SwRI Final Report to PM-ECW, William S. Williamson, Jr. Joseph H. 

 Brewer. 

3. Development and Evaluation of an Analytical Method for Determination of GB, VX, and 

 HD in Coral, SwRI Final Report to PM-ECW, William S. Williamson, Jr., Joseph H. 

 Brewer. 

4. Development and Evaluation of an Analytical Method for Determination of GB, VX, and 

 HD in Charcoal, SwRI Final Report to PM-ECW, Michael G. MacNaughton, Ph.D., P.E., 

 William S. Williamson, Jr., Joseph H. Brewer. 
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5. Development and Evaluation of an Analytical Method for Determination of GB, VX, and 

 HD on Surfaces, SwRI Final Report to PM-ECW, Carter Crigler. 

6. Laboratory Monitoring and Quality Assurance Plan dated June 2004, Department of 

 Army, Chemical Material Agency. 

17.0 TABLES, DIAGRAMS, FLOW CHARTS, AND VALIDATION DATA 

 There are no tables or figures associated with this method. 
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Appendix A:

Summary of Revisions to Method 3572 (as compared to previous Revision 0, July, 2007)

1. Improved overall method formatting for consistency with new SW-846 methods style 

guidance. The format was updated to Microsoft Word.docx. 

2. Sections 7.2 and 7.3, added the words “or equivalent” to Optima grade description as 

that is a trademarked term of Thermo/Fisher Scientific. Optima grade is a high purity 

gas chromatography grade of solvent. 

3. Updated VX stability information has been added to Sec. 8.2.4. 

4. LLOQ language added to Section 9.2. 

5. Minor editorial and technical revisions were made throughout to improve method clarity. 

The revision number was changed to one and the footer date to July 2014.